Acrylonitrile-butadiene-styrene copolymer resin (hereinafter ABS resin) generally has a good balance of physical properties such as processability of styrene, toughness and chemical resistance of acrylonitrile, and impact resistance of butadiene, and has an excellent appearance. Therefore, ABS resins have been widely used in automobile parts, electronic and electrical appliances, office appliances, electronic goods, toys, stationery goods and the like. However, ABS resins are typically opaque. Accordingly, other transparent resins such as SAN (Styrene-Acrylonitrile), PC (Polycarbonate), PS (Polystyrene), PMMA (Polymethyl methacrylate) and the like, have been primarily employed as materials for applications requiring transparency.
However, although SAN, PS and PMMA resins are superior in transparency and cost, they have poor impact resistance, which restricts their application range. For example, polycarbonate resin has low chemical resistance and high cost, thereby limiting applications for its use, although transparency and impact resistance are superior. Therefore, efforts have been made to provide a transparent ABS resin satisfying both transparency and impact resistance requirements.
Korea Patent Nos. 0429062, 0507336, and 0519116, Korea Patent Laid-open No. 2006-016853, U.S. Pat. No. 4,767,833, U.S. Patent Publication No. 2006/0041062, and Japanese Patent Laid-open No. 2006-63127 disclose that transparency can be obtained by adjusting the difference in refractive index between the dispersed phase and the continuous phase (matrix resin) to not more than 0.005 and that impact strength of the transparent ABS resin can be improved by using rubber particles or rubber-graft copolymer prepared using various methods.
It is known to make ABS resin transparent by minimizing the diffusion of the light in the visible wavelength region by adjusting the size of the rubber particles employed in ABS resin. Another known method is matching the refractive indices between the dispersed phase (rubber) and the continuous phase (matrix resin) to minimize the diffusion and refraction of the light at the interface between the dispersed phase and the continuous phase. The ABS resins prepared by using these methods may have a practical usable transparency.
However, in addition to transparency, impact strength and fluidity are also important factors in the process of preparing the transparent ABS resins. Transparent ABS resins should have good impact strength and fluidity properties for extrusion or injection processes used to mold a desired shape and for the general uses of the resultant product.
The foregoing technologies disclose that the impact strength of the transparent ABS resins can be improved by using rubber particles prepared in various methods; they do not, however, teach a method of improving impact strength of the transparent ABS resin which solves the problems during melt-mixing of the ABS resin with a matrix resin. Also, according to the foregoing technologies, methacrylic acid alkyl ester or acrylic acid alkyl ester, aromatic vinyl compound and unsaturated nitrile compound can be mixed and copolymerized to adjust refraction index. However, resins containing methacrylic acid alkyl ester or acrylic acid alkyl ester generally have a stiff polymer chain, which decreases the compatibility of the resin with the rubber phase.